Trauma and disease can lead to the complete or partial loss of tissue, or a whole organ. Surgical strategies to deal with tissue loss include organ transplantation from one individual to another, tissue transfer from a healthy site to the affected site in the same individual, and replacement of tissue function with mechanical devices such as prosthetic joints and dialysis machines. Additional strategies include pharmacologic supplementation of the metabolic products of absent or nonfunctional tissue.
These strategies have a number of inherent limitations. For example, supplementation of metabolic products of diseased organs is currently most commonly used in endocrinology. Hormonal products, such as insulin, thyroid, adrenal, or gonadal hormones can be continuously supplemented. The lack of normal feedback mechanisms, though, may result in an imbalance of hormone levels, causing acute or long-term complications.
Non-biological materials are used routinely in ophthalmology (e.g., intraocular lenses), traumatology (e.g., replacement of joints), cardiovascular surgery (e.g., mechanical heart valves, vascular prostheses, and stents), and reconstructive and cosmetic surgery. These materials are also used for extracorporeal devices, such as dialysis or plasmapheresis apparatuses. Major complications include infection, lack of biocompatibility and limited material durability.
Surgical reconstruction, such as using different organs, or unaffected tissue, to replace diseased tissue or organ, also has its limitations. The replacement organs may include different tissue types, may not be able to properly function in the new environment, and may be unable to completely replace lost function. Morbidity at the donor site is a major concern.
Organ transplantation of kidney, liver, heart, lung, and pancreas has made many innovative advances in recent years. Unfortunately, however, organ transplantation is severely limited by an increasing donor shortage. The other major problems are the high cost of the procedures, and the necessity of lifelong immunosuppression with its serious side effects.
On the other hand, the technique of tissue engineering seeks to replace or restore damaged or defective tissue and organs with constructs that include specific populations of living cells that meet the needs of the damaged portion of the recipient. A problem in the field of tissue engineering, however, is the provision of support structures, often called scaffolds, that physically support and promote the growth of different cell types, in vitro or in vivo, to form new tissue or organs. Preferably the scaffolds are resorbed by the cells which grow around and within them. Accordingly, the present invention provides structures useful, for example, for physically supporting growing tissue and organs in vitro and in vivo, and methods of making the structures.